Contextual hotwords

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for contextual hotwords are disclosed. In one aspect, a method, during a boot process of a computing device, includes the actions of determining, by a computing device, a context associated with the computing device. The actions further include, based on the context associated with the computing device, determining a hotword. The actions further include, after determining the hotword, receiving audio data that corresponds to an utterance. The actions further include determining that the audio data includes the hotword. The actions further include, in response to determining that the audio data includes the hotword, performing an operation associated with the hotword.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. patent application is a continuation of, and claims priorityunder 35 U.S.C. § 120 from, U.S. patent application Ser. No. 16/362,831,filed on Mar. 25, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/391,358, filed on Dec. 27, 2016. The disclosuresof these prior applications are considered part of the disclosure ofthis application and are hereby incorporated by reference in theirentireties.

FIELD

This specification generally relates to automated speech recognition.

BACKGROUND

The reality of a speech-enabled home or other environment—that is, onein which a user need only speak a query or command out loud and acomputer-based system will field and answer the query and/or cause thecommand to be performed—is upon us. A speech-enabled environment (e.g.,home, workplace, school, etc.) can be implemented using a network ofconnected microphone devices distributed throughout the various rooms orareas of the environment. Through such a network of microphones, a userhas the power to orally query the system from essentially anywhere inthe environment without the need to have a computer or other device infront of him/her or even nearby. For example, while cooking in thekitchen, a user might ask the system “how many milliliters in threecups?” and, in response, receive an answer from the system, e.g., in theform of synthesized voice output. Alternatively, a user might ask thesystem questions such as “when does my nearest gas station close,” or,upon preparing to leave the house, “should I wear a coat today?”

Further, a user may ask a query of the system, and/or issue a command,that relates to the user's personal information. For example, a usermight ask the system “when is my meeting with John?” or command thesystem “remind me to call John when I get back home.”

SUMMARY

For a speech-enabled system, the user's manner of interacting with thesystem is designed to be primarily, if not exclusively, by means ofvoice input. Consequently, the system, which potentially picks up allutterances made in the surrounding environment including those notdirected to the system, must have some way of discerning when any givenutterance is directed at the system as opposed e.g., to being directedan individual present in the environment. One way to accomplish this isto use a hotword, which by agreement among the users in the environment,is reserved as a predetermined word that is spoken to invoke theattention of the system. In an example environment, the hotword used toinvoke the system's attention are the words “OK computer.” Consequently,each time the words “OK computer” are spoken, it is picked up by amicrophone, conveyed to the system, which performs speech modelingtechniques to determine whether the hotword was spoken and, if so,awaits an ensuing command or query. Accordingly, utterances directed atthe system take the general form [HOTWORD] [QUERY], where “HOTWORD” inthis example is “OK computer” and “QUERY” can be any question, command,declaration, or other request that can be speech recognized, parsed andacted on by the system, either alone or in conjunction with the servervia the network.

In cases where the user provides several hotword based commands to aspeech-enabled system, such as a mobile phone, the user's interactionwith the phone may become awkward. The user may speak, “Ok computer,play my homework playlist.” The phone may begin to play the first songon the playlist. The user may wish to advance to the next song andspeak, “Ok computer, next.” To advance to yet another song, the user mayspeak, “Ok computer, next,” again. To alleviate the need to keeprepeating the hotword, the phone may be configured to recognize just“next” as both the hotword and the query, or in this instance, acommand. With this feature, the user's interaction with the phone andthe music application becomes more natural as the user only needs tospeak “next” to advance to the next song instead of “Ok computer, next.”

To accomplish this, the speech-enabled system determines a currentcontext of the system and identifies related hotwords. The context maybe based on an application that is running on the system, the locationof the system, the movement of the system, or any other similarsituation. The system may use the context of the system to identifyadditional hotwords. For example, when music is playing, the system mayidentify the hotwords “next,” “stop,” and “back” for controlling themusic. The system may request a hotword model for each of the identifiedhotwords. The system may use the hotword models to recognize the newhotwords by processing the audio characteristics of audio datacorresponding to the user's speech and applying the hotword models tothe audio characteristics. The system recognizes a spoken hotword, andperforms the corresponding operation. If the user speaks “stop” and“stop” is an active hotword because the system is playing music, thenthe system may stop playing music.

According to an innovative aspect of the subject matter described inthis application, a method for rollback resistant security includes theactions of determining, by a computing device, a context associated withthe computing device; based on the context associated with the computingdevice, determining a hotword; after determining the hotword, receivingaudio data that corresponds to an utterance; determining that the audiodata includes the hotword; and in response to determining that the audiodata includes the hotword, performing an operation associated with thehotword.

These and other implementations can each optionally include one or moreof the following features. The action of determining that the audio dataincludes the hotword includes determining that the audio data includesthe hotword without preforming speech recognition on the audio data. Theaction of determining that the audio data includes the hotword includesextracting audio features of the audio data that corresponds to theutterance; generating a hotword confidence score by processing the audiofeatures; determining that the hotword confidence score satisfies ahotword confidence threshold; and, based on determining that the hotwordconfidence score satisfies a hotword confidence threshold, determiningthat the audio data that corresponds to the utterance includes thehotword. The actions further include after determining the hotword,receiving a hotword model that corresponds to the hotword. The action ofdetermining that the audio data includes the hotword includesdetermining, using the hotword model, that the audio data includes thehotword.

The action of identifying, by the computing device, an application thatis running on the computing device. The context is based on theapplication that is running on the computing device. The actions furtherinclude determining, by the computing device, that the context is nolonger associated with the computing device; and determining thatsubsequently received audio data that includes the hotword is not totrigger an operation. The actions further include providing, for output,data identifying the hotword. The actions further include identifying,by the computing device, movement of the computing device. The contextis based on the movement of the computing device. The actions furtherinclude identifying, by the computing device, a location of thecomputing device. The context is based on the location of the computingdevice. The action of performing an operation associated with thehotword includes performing speech recognition on a portion of the audiodata that does not include the hotword. The operation is based on atranscription of the portion of the audio that does not include thehotword. The audio data only includes the hotword. An initial portion ofthe audio data includes the hotword.

Other embodiments of this aspect include corresponding systems,apparatus, and computer programs recorded on computer storage devices,each configured to perform the operations of the methods.

The subject matter described in this application may have one or more ofthe following advantages. A computing device may recognize and act inresponse to shorter commands that would typically require the user tospeak a hotword followed by the command. A computing device may be ableto recognize and act in response to different commands withoutperforming speech recognition on the commands. A computing device mayalso reduce computing resources required and battery power needed torecognize a query and a command because with the computing device mayrecognize a query and a command in one term.

The details of one or more embodiments of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system for identifying and processingcontextual hotwords.

FIG. 2 illustrates an example process for identifying and processingcontextual hotwords.

FIG. 3 illustrates an example of a computing device and a mobilecomputing device.

In the drawings, like reference numbers represent corresponding partsthroughout.

DETAILED DESCRIPTION

FIG. 1 illustrates an example system 100 for identifying and processingcontextual hotwords. Briefly, and as described in more detail below, thecomputing device 104 begins to play music in response to the utterance106, “Ok computer, play music.” The computing device 104 begins to playmusic, and the computing device 104 is able to recognize the additionalhotword “next” as an instruction to advance to the next song.

In more detail and beginning at stage A in FIG. 1, the user 102 speaksthe utterance 106, “Ok computer, play music” in the vicinity of thecomputing device 104. A microphone of the computing device 104 receivesthe utterance 104 and processes the audio data that corresponds to theutterance. The initial processing of the audio data may involvefiltering the audio data and converting the audio data from an analogsignal to a digital signal.

As the computing device 104 processes the audio data, the computingdevice may store the audio data in a buffer for additional processing.With the audio data in the buffer, the computing device 104 may identifywhether the audio data includes any spoken words. One way the computingdevice 104 identifies spoken words is to use a hotword detector 108. Thehotword detector 108 is configured to identify hotwords that areincluded in the audio data.

In some implementations, the hotword detector 108 may be configured toidentify hotwords that are in the initial portion of the utterance 106.In this example, the hotword detector 108 may determine that theutterance 106 “Ok computer, play music” includes the hotword 110 “okcomputer” if the hotword detector 108 detects acoustic features in theaudio data that are characteristic of an active hotword 112. Theacoustic features may be mel-frequency cepstral coefficients (MFCCs)that are representations of short-term power spectrums of the utteranceor may be mel-scale filterbank energies for the utterance 106. Forexample, the hotword detector 108 may detect that the utterance 106 “Okcomputer, play music” includes the hotword 110 “ok computer” based ongenerating MFCCs from the audio data and classifying that the MFCCsinclude MFCCs that are similar to MFCCs that are characteristic of thehotword “ok computer” as stored in the hotword models 114. As anotherexample, the hotword detector 108 may detect that the utterance 106 “Okcomputer, play music” includes the hotword 110 “ok computer” based ongenerating mel-scale filterbank energies from the audio data andclassifying that the mel-scale filterbank energies include mel-scalefilterbank energies that are similar to mel-scale filterbank energiesthat are characteristic of the hotword “ok computer” as stored in thehotword models 114.

The hotword detector 108 determines that the audio data that correspondsto the utterance 106 includes the hotword 110, and the computing device104 may perform speech recognition or semantic interpretation on theaudio data that corresponds to the utterance 106. The speech recognizer116 may perform speech recognition on the portion of the audio data thatfollows the hotword 110. In this example, the speech recognizer 116 mayidentify the words 118 “play music.”

In some implementations, the speech recognizer 116 may not be located onthe computing device 104. Instead, the computing device 104 provides theaudio data that corresponds to the portion of the utterance 106 afterthe hotword 110 to a server, for example, server 120. The server 120performs speech recognition and returns a transcription of the audiodata to the computing device 104. The computing device 104 identifiesthe words in the utterance 106, and the computing device performssemantic interpretation and identifies any speech commands. Thecomputing device 104 identifies the command and executes the command. Inthis example and in stage B, the computing device 104 beings to playmusic 122 upon identifying the “play music” command 118.

With the music playing 122 the computing device 104 is running a musicapplication in either the foreground or the background. The computingdevice 104 may include a context identifier 124 and an active hotwordselector 126. The context identifier 124 may be configured to identify acurrent context of the computing device 104. The active hotword selector126 may use the current context of the computing device 104 to selectactive hotwords. In this example, the context of the device may berelated to playing music 122 and running the music application. Theactive hotword selector 126 may examine the code of the musicapplication to identify any hotwords that the developers of the musicapplication want users to be able to speak to interact with the musicapplication and the respective actions for each hotword. The musicapplication may identify hotwords such as “play,” “next,” “stop,” and“back.” Based on the context of music actively playing the activehotword selector 126 may select the hotwords of “next,” “stop,” and“back” and store them in the active hotwords 112.

In some implementations, the context identifier 124 may use the locationof the computing device 104 to determine the context. For example, thecontext identifier 124 may determine that the location corresponds tothe home of the user 102 of the computing device 104. The active hotwordselector 126 may use the context that the device is at the home of theuser 102 to identify hotwords such as “warmer” and “cooler” to allow theuser to control the temperature of the home. Similar to the exampleabove, the active hotword selector 126 may store the “warmer” and“cooler” hotwords in the active hotwords 112 while the user 102 is athome.

In some implementations, the context identifier 124 may use the motionof the computing device 104 to determine the context. For example, thecontext identifier 124 may determine that the movement of the computingdevice 104 corresponds to the speed and motion of a typical vehicle. Thecontext identifier 124 may also compare the speed and motion of thecomputing device 104 to determine whether the computing device 104 ismoving along a road to increase the confidence that the computing device104 is in a vehicle. In this instance, the active hotword selector 126may use the context of computing device to identify the hotword“directions” to allow the user to request directions to a particularlocation. The active hotword selector 126 may store the hotword“directions” in the active hotwords 112 while the computing device 104is in the vehicle.

In some implementations, the context identifier 124 may use the day ortime or both to determine the context. For example, the contextidentifier 124 may determine that the context corresponds to the eveninghours, such as between 9:00 pm and midnight. In this instance, theactive hotword selector 126 may use the context of evening hours toidentify the hotword “set alarm” to allow the user 102 to set an alarm.The active hotword selector 126 may store the hotword “set alarm” in theactive hotwords 112 during the 9:00 pm to midnight time period.

In some implementations, the context identifier 124 may use the pastactions and patterns of the user 102 to identify hotwords. The contextidentifier 124 may identify actions that the user typically performs,perhaps at different times of the day, and determine a context based onthose actions. The active hotword selector 126 may identify relatedhotwords and store those hotwords in the active hotwords 112 during thecorresponding time period. For example, the context identifier 124 maydetermine that the user 102 reads the news on the computing device 104during the hours of 8:00 am to 10:00 am. The active hotword selector 126may select “news” as an active hotword 112. With “news” as a hotword,the user 102 may say “news” to open the news application during thehours of 8:00 am to 10:00 am. The news application may have its owncorresponding hotwords. The active hotword selector 126 may identifyhotwords such a “sports,” “local,” and “national” as active hotwords 112when the news application is open on the computing device 104.

In some implementations, the context identifier 124 may identify pastactions that may not necessarily be time dependent. For example, theuser 102 may habitually check the weather on the computing device 102.The context identifier 124 may determine that the context of thecomputing device almost always corresponds a time when the user 102 haschecked the weather. In this case, the active hotword selector 126 mayidentify the hotword “weather” and store the hotword in the activehotwords 112. With “weather” as an active hotword, the user 102 justspeaks “weather” to open a weather application and check the weather.

In some implementations, the context identifier 124 may determine acontext based on a state of the computing device 104. For example, thestate of the computing device 104 may be “locked.” In this case, theactive hotword selector 126 may identify the hotword “unlock” and storethe hotword in the active hotwords 112 when the device is locked. With“unlock” as an active hotword, the user speaks “unlock” to unlock thephone. In order to improve security, the computing device 104 may usespeaker identification techniques to verify that the speaker is the user102. In this case, a corresponding hotword model would be trained usingspeech of the user 102. For example, the computing device 104 may promptthe user 102 to speak “unlock” several times so that the computingdevice 104 or server 120 can build a hotword model specific to user 102with the speech samples.

The active hotwords 112 include a new hotword, and the computing device104 may check the hotword models 114 to determine if the computingdevice 104 has a hotword for the newly added hotword. For example, thecomputing device 104 may check whether the hotword models 114 includes ahotword model for “next” when the active hotword selector 126 stores“next” in the active hotwords 112. If the hotword model for “next” is inthe hotword models 114, then the hotword detector 108 can begindetecting the hotword “next,” and the computing device 104 can skipstages C, D, and E. If the hotword model for “next” is not in thehotword models 114, then the computing device 104, in stage C, sends arequest 128 to server 120 for the hotword model for “next.”

In some implementations, the computing device 104 may request a hotwordmodel for a hotword word that already has a corresponding hotword modelin the hotword models 114. The computing device 104 may request ahotword model periodically, such as once per week, to ensure that thelocally stored hotword model is as accurate as possible. The computingdevice 104 may also request a hotword model in response to feedback fromthe user 102. In some instances, the user 102 may speak a hotword suchas “next” and the computer may not advance the song. The hotworddetector 108 may process the audio data corresponding to “next” but maynot identify the hotword because the hotword confidence score did notsatisfy a threshold.

The user 102 may advance the song by selecting the next song button onthe computing device 104. When the computing device 104 detects thisseries of actions, the computing device 104 may request an undatedhotword model for “next.” Alternatively, the computing device 104 mayupdate the hotword model for “next” using the audio data that did notgenerate a hotword confidence score that satisfy the threshold but wasabove a lower hotword confidence threshold. In some implementations, thecomputing device 104 may calculate a noise level for the audio data thatdid not generate a hotword confidence score that satisfy the threshold.If the noise level is greater than a noise threshold, then the computingdevice 104 may not update the hotword model with the corresponding audiodata since it may have too much background noise.

The server 120 receives the request 128 for the hotword model andidentifies the corresponding hotword model 130 in stage D. The server120 may correspond to one or more servers that are accessible through anetwork 132 such as the internet. The data accessible by one server maybe accessible by other servers. In addition to identifying and providinghotword models, the server 120 is configured to receive audio data andgenerate hotword models 130 based on the received audio data.

To generate hotword models 130, the server 120 receives and collectsspeech data 134. The server 120 may receive speech data 134 from serversthat perform speech recognition. The servers may perform the speechrecognition and provide the audio data to the server 120 to generatehotword models. With the collected speech data 134, the speechrecognizer 136 identifies the words in the collected speech data.

The speech recognizer 136 provides the transcription and the speech datato the speech data tokenizer 138. The speech data tokenizer 138 segmentsthe audio data into portions that correspond to different words. Forexample, if the collected speech data 134 corresponds to the words “playthe next song,” then the speech recognizer generated the transcriptionof “play the next song” and the speech data tokenizer 138 tokenizes theaudio data into four sections. There is one section for “play,” anothersection for “the,” another section for “next,” and another section for“song.”

The speech recognizer 136 and speech data tokenizer 138 may tokenizemany speech samples and provide the tokenized speech samples to thehotword model generator 140. The hotword model generator 140 processesmultiple samples of the same word to generate a hotword model for thatword. For example, the hotword model generator 140 may receive multiplespeech samples that correspond to the word “next.” The hotword modelgenerator 140 extracts the audio characteristics of the speech sample togenerate the hotword model for “next.” The hotword model generator 140stores the hotword model for “next” in the hotword models 130.

The hotword models 130 are ready for the server 120 to provide tocomputing devices to recognize those particular hotwords. In someimplementations the server 120 may not have the requested hotword in thehotword models 130. In this case, the server 120 may analyze thecollected speech data 134 using the speech recognizer 136 and speechdata tokenizer 138 to identify audio samples that correspond to therequested word. Alternatively, the server 120 may request that thecomputing device 104 collect samples. The computing device 104 mayrequest the user to repeat a word several times. The computing device104 may provide the audio data to the server 120 for processing togenerate a hotword model. In some implementations, a requested hotwordmay be more than one word. In this instance, the hotword model generator140 may combine hotword models 130 to generate a hotword model for themultiple word hotword.

In some implementations, the hotword model generator 140 may generatehotword models that include noise that is specific to a particularcontext. The hotword model generator 140 may not select all speechtokens that correspond to the target hotword. Instead, the hotword modelgenerator 140 select that speech tokens that include background noisethat is likely to exist in the corresponding context. For example, thehotword model generator 140 may generate a hotword model for “next” withspeech tokens that include “next” and have background music. If theserver 120 receives a request for the hotword model “next” and therequest indicates that the context is music playing, then the server 120may provide the hotword model of “next” that is configured forbackground music. If the server 120 receives a request for the hotwordmodel “next” and the request indicates that the context is photoviewing, then the server 120 may provide the hotword model of “next”that is configured for no background noise.

In stage E, the server 120 provides the response 142 that includes therequested hotword model. In the example shown in FIG. 1, the server 120provides a hotword model for “next” to the computing device 104. Thecomputing device 104 stores the hotword model in the hotword word models114 and may update an indicator in the active hotwords 112 to indicatethat there is a corresponding hotword model stored on the computingdevice 104.

In some implementations, the active hotword selector 126 may removehotwords from the active hotwords 112. When the context identifier 124indicates that the context has changed, the active hotword selector 126may update the active hotwords 112 based on the new context. Followingsome of the examples from above, the active hotword selector 126 mayremove the hotword “news” from the active hotwords 112 after 10:00 am.Similarly, the active hotword selector 126 may remove the hotword “setalarm” after midnight and add the hotword “set alarm” back to the activehotwords 112 after 9:00 pm. In some implementations, the correspondinghotword model remains in the hotword models 114 when the active hotwordselector 126 removes the hotword active hotwords 112.

In some implementations, the active hotword selector 126 may removehotwords from the active hotwords 112 even when the same application isrunning on the computing device 104. When the computing device 104executes the music application, the active hotword selector 126 mayidentify the hotwords “play,” “next,” “stop,” and “back” and load thecorresponding hotword models in the hotword models 114. In thisinstance, the hotwords need not be added to the active hotwords 112 forthe computing device 104 to request a hotword model. With the musicplaying, the active hotword selector 126 may include the hotwords“next,” “stop,” and “back” as the active hotwords. If the music stopsand the music application remains open, then the active hotword selector126 may update the active hotwords 112 to “next,” “play,” and “back.”

In some implementations the user interface generator 144 generates auser interface for display on the computing device 104. The userinterface may indicate the active hotwords 112. For example, the userinterface may indicate, when a song begins to play, for the user 102 tosay “next,” “stop,” or “back” to control the music. When the musicstops, the user interface may indicate that the user 102 can say “next,”“play,” and “back” to control the music. The user interface generator144 may also generate a notification when a hotword is active.

For example, the user interface may indicate that the hotword set“alarm” is active when the current time reaches 9 pm. Similarly, theuser interface may indicate that the hotword “set alarm” is no longeractive when the current time reaches midnight. The user interface mayalso indicate the effect of speaking each hotword. For example, when themusic application is active and the music is playing the user interfacemay indicate that “next” advances to the next song in the playlist,“stop” stops the current song from playing, and “back” returns to theprevious song in the playlist.

In some implementations, the user interface generator 144 may alsogenerate a user interface to control when different hotwords are active.The control interface may include the context when a hotword is activeand allow the user to update the context when a hotword is active.Additionally or alternatively, the control interface may allow the user102 to indicate the hotwords that are active for each context. Forexample, the control interface may indicate that the hotword “news” isactive from 8:00 am to 10:00 am. The user 102 may adjust that context sothat the “news” hotword is active from 8:00 am to noon.

The control interface may also indicate that the hotwords “next,”“stop,” or “back” are active when music is playing. The user 102 mayupdate the hotwords for the music playing context to only be “next” and“stop.” In some implementations, the control interface may also providethe user 102 the capability to add custom hotwords for existing orcustom contexts. For example, the user 102 may input into the controlinterface “call mom” as a hotword, always have the hotword active, andupon detecting the hotword to call the contact “mom.” The user 102 mayalso add “up” and “down” to the music playing context and specify thatthe hotwords control the volume. The user may also add a new contextthat corresponds to the time period 11:00 am to 1:00 pm. The user mayadd the hotword “order lunch” to be active during that time period andindicate that the hotword is to open a food ordering application.

At stage F, the user 102 speaks the utterance 146 that includes thehotword 148. The computing device 104 receives the utterance 146 throughthe microphone and processes the corresponding audio data. The hotworddetector 108 compares the hotword models 114 of the active hotwords 112to identify whether the utterance 146 includes any active hotwords. Ifthe hotword detector 108 identifies a hotword, then the computing deviceperforms the corresponding command. In the example shown in FIG. 1, theuser 102 speaks “next.” The active hotwords 112 may be “stop,” “next,”and “back.” The hotword detector 108 compares the audio data thatcorresponds to utterance 146 to the hotword models 114 that correspondto “stop,” “next,” and “back” and determines that the utterance 146includes the hotword “next.” Based on detecting the hotword “next” thatcorresponds to the instruction to advance to the next song, thecomputing device advances to the next song 150 at stage G.

In some implementations, the hotword detector 108 may detect hotwordsthat are not among the active hotwords 112 but whose models are stillstored in the hotword models. In this instance, the hotword detector 108may provide an indication to the user interface generator 144 togenerate a user interface indicating that the hotword is not currentlyactive. For example, the user 102 may speak “play” when the music isplaying. The hotword detector 108 may identify the hotword “play.”Because the hotword is not active the computing device 104 performs noaction. However, the user interface generator 144 may generate aninterface indicating that the hotword “play” is not active andindicating the active hotwords are “stop,” “next,” and “back.”

In some implementations, the computing device 104 may still beconfigured to identify the default hotword “ok computer.” In thisinstance, the computing device 104 may process the audio data thatfollows “ok computer” using speech recognition and execute theappropriate action based on transcription of the subsequent audio data.For example, if the user 102 speaks “ok computer, next” while music isplaying, then the computing device 104 advances to the next song afteridentifying the “ok computer” hotword and transcribing the subsequentportion of the audio data that includes the command “next.”

Similarly, the contextual hotwords can be followed by commands.Continuing with the “order lunch” example, the user 102 may speak “orderlunch from Sandwich Deli” during the time when the hotword is active. Inthis instance, the hotword detector 108 identifies the “order lunch”hotword. The speech recognizer 116 generates the transcription “fromSandwich Deli.” The computing device 104 may open the food orderingapplication and open the Sandwich Deli menu.

In some implementations, the hotword detector 108 generates a hotwordconfidence score for each initial portion of processed audio data. Ifthe hotword confidence score satisfies a threshold, then the hotworddetector 108 determines that the audio data includes the hotword. Forexample, if the hotword confidence score is 0.9 and the hotwordconfidence threshold is 0.8, then the hotword detector 108 determinesthat the audio data includes the hotword.

In some implementations, if the hotword confidence score is with a rangebelow the threshold, then the user interface generator 144 may generatean interface asking for confirmation that the user 102 spoke thehotword. For example, the hotword confidence score may be 0.7. If therange is between 0.6 and 0.8, then the user interface generator 144 maygenerate a user interface requesting that the user 102 confirm or repealthe hotword. In some implementations and if the user 102 confirms thatthe user 102 spoke the hotword, the computing device 104 may use theaudio data to update the hotword model to improve performance in thefuture. The computing device 104 may not use the audio data if there istoo much noise in the audio data.

FIG. 2 illustrates an example process 200 for identifying and processingcontextual hotwords. In general, the process 200 identifies hotwordsbased on a context of the device and assigns actions to the hotwords sothat when a user speaks the hotword, the process performs thecorresponding action. The process 200 will be described as beingperformed by a computer system comprising at one or more computers, forexample, system 100 as shown in FIG. 1.

The system determines a context associated with the computing device(210). In some implementations, the system identifies an applicationthat is running on the system. The system determines the context basedon the application that is running on the system. For example, theapplication may be a music application. In this case, the context may beplaying music. The system may also distinguish between applicationsrunning in the background and the foreground. For example, the musicapplication running and playing music in the background or theforeground may still have the same context of playing music. Anapplication such as a browser running in the background may not affectthe context. In some implementations, the context may also be related toa state of the device such as when the device is locked. The context mayalso be related to what is displayed on the screen, for example, “homescreen.”

In some implementations, the context may be based on the movement of thesystem. For example, if the system is moving at speeds that are similarto a car, then the system may determine that the context is “in a car.”In some implementations, the context may be based on a location of thecomputing device. For example, the system may be located at a home ofthe user. In this case, the context of the device may be “at home.” Insome implementations, the context may be a combination of contexts. Forexample, the context may be “locked at home” for when the system islocked and at the home of the user.

The system, based on the context associated with the system, determinesa hotword (220). In some implementations, system determines a hotwordbased on hotwords identified in software. For example, the musicapplication may identify hotwords for when the context is “musicplaying” and when the music is stopped and the music application isopen.

In some implementations, the system may determine hotwords based onprior use. For example, if the user typically reads the news during acertain time range, then the system may determine the hotword “news” forwhen the context is in that time range. In some implementations, thesystem may display the hotword and indicate in the display the actionperformed by the hotword. The system may provide notification when thehotword becomes active and when the system deactivates it.

The system, after determining the hotword, receives audio data thatcorresponds to an utterance (230). In some implementations, the systemrequests a hotword model for the hotword from a server, and the systemdetermines the hotword. For example, if the system determines thehotword “next,” then the system may request from a server a hotwordmodel for “next.”

The system determines that the audio data includes the hotword (240). Insome implementations, the system determines that the audio data includesthe hotword without performing speech recognition on the audio data. Insome implementations, the system determines that the audio data includesthe hotword by extracting audio features of the audio data thatcorresponds to the utterance. The system generates a hotword confidencescore by processing the audio features and possibly by comparing theaudio features to those in a hotword model.

If the hotword confidence score satisfies a hotword confidencethreshold, then the system determines that the audio data includes thehotword. If the hotword confidence score does not satisfy the hotwordconfidence threshold, then the system determines that the audio datadoes not include the hotword. For example, if the hotword confidencethreshold is 0.8, then audio data with a hotword confidence score above0.8 would be labeled as including the hotword and audio data withhotword confidence score below 0.8 would be labeled as not including thehotword.

In some implementations, the audio data only includes the hotword. Forexample, the user may only speak “next,” which is a hotword. In someimplementations, an initial portion of the audio data includes thehotword. For example, the hotword may be “order lunch” and the user mayspeak “order lunch from Sandwich Deli.” In this instance, the systemidentifies the hotword “order lunch” and processes the portion of theaudio data that follows the hotword using speech recognition.

The system, in response to determining that the audio data includes thehotword, performs an operation associated with the hotword (250). Insome implementations, the system identifies the action using thehotword. For example, when music is playing and the user speaks “next,”the system advances the song.

In some implementations, the system removes a hotword from the activehotwords list when the context is no longer valid. For example, if theuser stops playing music, then the system removes the hotword “next”from the list of active hotwords. If a user speaks “next” in this case,then the system performs no action in response to “next.”

In some implementations, the operation may be based on the hotword andany audio data that follows the hotword or only on the audio data thatfollows the hotword. For example, an active hotword may be “directions”and the user may speak “directions home.” In this case, the system mayopen the mapping application and begin to provide the user directions tothe user's home.

In some implementations, the operation may be dependent on the audiodata that follows a hotword. There may be instances where an activehotword may have different operations depending on the audio data thatfollows the hotword. For example, a user may be at home and the systemmay be playing music. The user being at home may cause the system toactivate the hotword “increase” to increase the temperature of thethermostat. The system playing music may also cause the system toactivate the hotword “increase” to increase the volume of the music. Inthis case, the system may alleviate this conflict in one or more of thefollowing ways.

The system may update the hot words to be “increase temperature” and“increase volume”. The system may display an indication on the screen ifthe user says “increase” that the user should speak “increase volume” toincrease the music volume or “increase temperature” to increase thetemperature of the thermostat. Alternatively, the system may keep“increase” as a hotword and require an argument after the “increase”where the system performs speech recognition on any audio data after“increase” or request clarification from the user. For example, the usermay speak “increase.” The system may display a request or playsynthesized speech of the request for the user to clarify what toincrease.

In some implementations, the system may perform detect active hotwordsin the presence of an argument or suffix to the spoken hotword,sometimes only in the presence of an argument or suffix to the spokenhotword. For example, an active hotword may be “set alarm.” The systemmay only acknowledge the hotword “set alarm” when it is followed by anargument such as “for 6:00 am” or “for tomorrow morning.” In this case,the system may perform speech recognition on the portion of the audiodata that follows the hotword and not acknowledge the hotword unless thehotword is followed by additional spoken terms. In some implementations,the additional spoken terms are arguments that the hotword accepts. Thehotword “set alarm” may accept arguments such as “for 6:00 am” but not“tuna sandwich.”

In some implementations, the system may determine that the audio dataincludes more than one hotword. This may happen because currently activehotwords sound similar. For example, two active hotwords may be “next”and “text.” In some implementations, the system may only determine thatthe audio data includes a hotword, not necessarily which hotword. If thesystem determines that two or more hotword models match the audio data,then the system may perform speech recognition on the portion of theaudio data that includes the hotword to determine what hotword the userspoke.

FIG. 3 shows an example of a computing device 300 and a mobile computingdevice 350 that can be used to implement the techniques described here.The computing device 300 is intended to represent various forms ofdigital computers, such as laptops, desktops, workstations, personaldigital assistants, servers, blade servers, mainframes, and otherappropriate computers. The mobile computing device 350 is intended torepresent various forms of mobile devices such as personal digitalassistants, cellular telephones, smart-phones, and other similarcomputing devices. The components shown here, their connections andrelationships, and their functions, are meant to be examples only, andare not meant to be limiting.

The computing device 300 includes a processor 302, a memory 304, astorage device 306, a high-speed interface 308 connecting to the memory304 and multiple high-speed expansion ports 310, and a low-speedinterface 312 connecting to a low-speed expansion port 314 and thestorage device 306. Each of the processor 302, the memory 304, thestorage device 306, the high-speed interface 308, the high-speedexpansion ports 310, and the low-speed interface 312, are interconnectedusing various busses, and may be mounted on a common motherboard of inother manners as appropriate. The processor 302 can process instructionsfor execution within the computing device 300, including instructionsstored in the memory 304 or on the storage device 306 to displaygraphical information for a GUI on an external input/output device, suchas a display 316 coupled to the high-speed interface 308. In otherimplementations, multiple processors and/or multiple buses may be used,as appropriate, along with multiple memories and types of memory. Alsomultiple computing devices may be connected, with each device providingportions of the necessary operations (e.g., as a server bank, a group ofblade servers, or a multi-processor system).

The memory 304 stores information within the computing device 300. Insome implementations, the memory 304 is a volatile memory unit or units.In some implementations, the memory 304 is a non-volatile memory unit orunits. The memory 304 may also be another form of computer-readablemedium such as a magnetic or optical disk.

The storage device 306 is capable of providing mass storage for thecomputing device 300. In some implementations, the storage device 306may be or contain a computer-readable medium, such as a floppy diskdevice, a hard disk device, an optical disk device, or a tape device, aflash memory or other similar solid state memory device, or an array ofdevices, including devices in a storage area network or otherconfigurations. Instructions can be stored in an information carrier.The instructions, when executed by one or more processing devices (forexample, processor 302), perform one or more methods, such as thosedescribed above. The instructions can also be stored by one or morestorage devices such as computer- or machine-readable mediums (forexample, the memory 304, the storage device 306, or memory on theprocessor 302).

The high-speed interface 308 manages bandwidth-intensive operations forthe computing device 300, while the low-speed interface 312 manageslower bandwidth-intensive operations. Such allocation of functions is anexample only. In some implementations, the high-speed interface 308 iscoupled to the memory 304, the display 316 (e.g., through a graphicsprocessor or accelerator), and to the high-speed expansion ports 310,which may accept various expansion cards. In the implementation, thelow-speed interface 312 is coupled to the storage device 306 and thelow-speed expansion port 314. The low-speed expansion port 314, whichmay include various communication ports (e.g., USB, Bluetooth, Ethernet,wireless Ethernet) may be coupled to one or more input/output devices,such as a keyboard, a pointing device, a scanner, or a networking devicesuch as a switch or router, e.g., through a network adapter.

The computing device 300 may be implemented in a number of differentforms, as shown in the figure. For example, it may be implemented as astandard server 320, or multiple times in a group of such servers. Inaddition, it may be implemented in a personal computer such as a laptopcomputer 322. It may also be implemented as part of a rack server system324. Alternatively, components from the computing device 300 may becombined with other components in a mobile device such as a mobilecomputing device 350. Each of such devices may contain one or more ofthe computing device 300 and the mobile computing device 350, and anentire system may be made up of multiple computing devices communicatingwith each other.

The mobile computing device 350 includes a processor 352, a memory 364,an input/output device such as a display 354, a communication interface366, and a transceiver 368, among other components. The mobile computingdevice 350 may also be provided with a storage device, such as amicro-drive or other device, to provide additional storage. Each of theprocessor 352, the memory 364, the display 354, the communicationinterface 366, and the transceiver 368, are interconnected using variousbuses, and several of the components may be mounted on a commonmotherboard or in other manners as appropriate.

The processor 352 can execute instructions within the mobile computingdevice 350, including instructions stored in the memory 364. Theprocessor 352 may be implemented as a chipset of chips that includeseparate and multiple analog and digital processors. The processor 352may provide, for example, for coordination of the other components ofthe mobile computing device 350, such as control of user interfaces,applications run by the mobile computing device 350, and wirelesscommunication by the mobile computing device 350.

The processor 352 may communicate with a user through a controlinterface 358 and a display interface 356 coupled to the display 354.The display 354 may be, for example, a TFT (Thin-Film-Transistor LiquidCrystal Display) display or an OLED (Organic Light Emitting Diode)display, or other appropriate display technology. The display interface356 may comprise appropriate circuitry for driving the display 354 topresent graphical and other information to a user. The control interface358 may receive commands from a user and convert them for submission tothe processor 352. In addition, an external interface 362 may providecommunication with the processor 352, so as to enable near areacommunication of the mobile computing device 350 with other devices. Theexternal interface 362 may provide, for example, for wired communicationin some implementations, or for wireless communication in otherimplementations, and multiple interfaces may also be used.

The memory 364 stores information within the mobile computing device350. The memory 364 can be implemented as one or more of acomputer-readable medium or media, a volatile memory unit or units, or anon-volatile memory unit or units. An expansion memory 374 may also beprovided and connected to the mobile computing device 350 through anexpansion interface 372, which may include, for example, a SIMM (SingleIn Line Memory Module) card interface. The expansion memory 374 mayprovide extra storage space for the mobile computing device 350, or mayalso store applications or other information for the mobile computingdevice 350. Specifically, the expansion memory 374 may includeinstructions to carry out or supplement the processes described above,and may include secure information also. Thus, for example, theexpansion memory 374 may be provided as a security module for the mobilecomputing device 350, and may be programmed with instructions thatpermit secure use of the mobile computing device 350. In addition,secure applications may be provided via the SIMM cards, along withadditional information, such as placing identifying information on theSIMM card in a non-hackable manner.

The memory may include, for example, flash memory and/or NVRAM memory(non-volatile random access memory), as discussed below. In someimplementations, instructions are stored in an information carrier, thatthe instructions, when executed by one or more processing devices (forexample, processor 352), perform one or more methods, such as thosedescribed above. The instructions can also be stored by one or morestorage devices, such as one or more computer- or machine-readablemediums (for example, the memory 364, the expansion memory 374, ormemory on the processor 352). In some implementations, the instructionscan be received in a propagated signal, for example, over thetransceiver 368 or the external interface 362.

The mobile computing device 350 may communicate wirelessly through thecommunication interface 366, which may include digital signal processingcircuitry where necessary. The communication interface 366 may providefor communications under various modes or protocols, such as GSM voicecalls (Global System for Mobile communications), SMS (Short MessageService), EMS (Enhanced Messaging Service), or MMS messaging (MultimediaMessaging Service), CDMA (code division multiple access), TDMA (timedivision multiple access), PDC (Personal Digital Cellular), WCDMA(Wideband Code Division Multiple Access), CDMA2000, or GPRS (GeneralPacket Radio Service), among others. Such communication may occur, forexample, through the transceiver 368 using a radio-frequency. Inaddition short-range communication may occur, such as using a Bluetooth,WiFi, or other such transceiver. In addition, a GPS (Global PositioningSystem) receiver module 370 may provide additional navigation- andlocation-related wireless data to the mobile computing device 350, whichmay be used as appropriate by applications running on the mobilecomputing device 350.

The mobile computing device 350 may also communicate audibly using anaudio codec 360, which may receive spoken information from a user andconvert it to usable digital information. The audio codec 360 maylikewise generate audible sound for a user, such as through a speaker,e.g., in a handset of the mobile computing device 350. Such sound mayinclude sound from voice telephone calls, may include recorded sound(e.g., voice messages, music files, etc.) and may also include soundgenerated by applications operating on the mobile computing device 350.

The mobile computing device 350 may be implemented in a number ofdifferent forms, as shown in the figure. For example, it may beimplemented as a cellular telephone 380. It may also be implemented aspart of a smart-phone 382, personal digital assistant, or other similarmobile device.

Various implementations of the systems and techniques described here canbe realized in digital electronic circuitry, integrated circuitry,specially designed ASICs (application specific integrated circuits),computer hardware, firmware, software, and/or combinations thereof.These various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms machine-readable medium andcomputer-readable medium refer to any computer program product,apparatus and/or device (e.g., magnetic discs, optical disks, memory,Programmable Logic Devices (PLDs)) used to provide machine instructionsand/or data to a programmable processor, including a machine-readablemedium that receives machine instructions as a machine-readable signal.The term machine-readable signal refers to any signal used to providemachine instructions and/or data to a programmable processor.

To provide for interaction with a user, the systems and techniquesdescribed here can be implemented on a computer having a display device(e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor)for displaying information to the user and a keyboard and a pointingdevice (e.g., a mouse or a trackball) by which the user can provideinput to the computer. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback (e.g., visual feedback,auditory feedback, or tactile feedback); and input from the user can bereceived in any form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in acomputing system that includes a back end component (e.g., as a dataserver), or that includes a middleware component (e.g., an applicationserver), or that includes a front end component (e.g., a client computerhaving a graphical user interface or a Web browser through which a usercan interact with an implementation of the systems and techniquesdescribed here), or any combination of such back end, middleware orfront end components. The components of the system can be interconnectedby any form or medium of digital data communication (e.g., acommunication network). Examples of communication networks include alocal area network (LAN), a wide area network (WAN), and the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

Although a few implementations have been described in detail above,other modifications are possible. For example, while a clientapplication is described as accessing the delegate(s), in otherimplementations the delegate(s) may be employed by other applicationsimplemented by one or more processors, such as an application executingon one or more servers. In addition, the logic flows depicted in thefigures do not require the particular order shown, or sequential order,to achieve desirable results. In addition, other actions may beprovided, or actions may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

What is claimed is:
 1. A method comprising: receiving, at dataprocessing hardware of a computing device, audio data corresponding to afirst utterance spoken by a user associated with the computing device,the first utterance comprising a default hotword followed by a commandto playback music from the computing device; detecting, by the dataprocessing hardware, the default hotword in the audio data correspondingto the first utterance spoken by the user, the detection of the defaulthotword in the audio data causing a speech recognizer to perform speechrecognition on the audio data to identify the command to playback themusic from the computing device; in response to the speech recognizerperforming speech recognition on the audio data to identify the commandto playback the music, executing, by the data processing hardware, thecommand to playback the music from the computing device; and duringplayback of the music from the computing device: activating, by the dataprocessing hardware, a set of additional hotwords each associated with arespective action for controlling the playback of the music from thecomputing device; restricting, by the data processing hardware, theactivated set of additional hotwords to a subset of the activated set ofadditional hotwords based on a playback state during the playback of themusic from the computing device; receiving, at the data processinghardware, additional audio data corresponding to a second utterancespoken by the user, the second utterance comprising one of theadditional hotwords in the subset of the activated set of additionalhotwords; detecting, by the data processing hardware, the additionalhotword in the additional audio data corresponding to the secondutterance spoken by the user; and based on detecting the additionalhotword in the additional audio data corresponding to the secondutterance, performing, by the data processing hardware, the respectiveaction associated with the detected additional hotword for controllingthe playback of the music from the computing device.
 2. The method ofclaim 1, wherein detecting the default hotword in the audio datacorresponding to the first utterance comprises detecting the defaulthotword in the audio data without performing speech recognition on theaudio data.
 3. The method of claim 1, wherein the speech recognizerexecutes on the data processing hardware of the computing device.
 4. Themethod of claim 1, further comprising, in response to detecting thedefault hotword in the audio data corresponding to the first utterancespoken by the user, providing, by the data processing hardware, theaudio data corresponding to the first utterance to a server incommunication with the data processing hardware, the server executingthe speech recognizer to perform the speech recognition on the audiodata to identify the command to playback the music from the computingdevice.
 5. The method of claim 1, wherein detecting the additionalhotword in the additional audio data corresponding to the secondutterance comprises detecting the additional hotword in the additionalaudio data without performing speech recognition on the additional audiodata.
 6. The method of claim 1, wherein detecting the additional hotwordin the additional audio data corresponding to the second utterancecomprises: extracting audio features of the additional audio data thatcorresponds to the second utterance; generating, using a hotworddetector, hotword confidence score by processing the extracted audiofeatures; determining, by the hotword detector, whether the hotwordconfidence score satisfies a hotword confidence threshold; and when thehotword confidence score satisfies the hotword confidence threshold,determining, by the hotword detector, that the additional audio datacorresponding to the second utterance includes the additional hotword.7. The method of claim 6, further comprising, when the hotwordconfidence score fails to satisfy the hotword confidence threshold:determining, by the hotword detector, that the additional audio datadoes not include the additional audio data corresponding to the secondutterance does not include the additional hotword; and bypassing, by thedata processing hardware, performing the respective action forcontrolling the playback of the music from the computing device.
 8. Themethod of claim 1, wherein the second utterance only comprises the oneof the additional hotwords in the subset of the activated set ofadditional hotwords.
 9. The method of claim 1, wherein each additionalhotword in the activated set of additional hotwords is associated with arespective hotword model configured to recognize audio of the respectiveadditional hotword.
 10. The method of claim 1, further comprisingstoring, by the data processing hardware, multiple hotword models onmemory hardware of the computing device, each hotword model of themultiple hotword models associated with a respective one of theadditional hotwords in the activated set of additional hotwords that isconfigured to recognize audio of the respective one of the additionalhotwords.
 11. A computing device comprising: data processing hardware;and memory hardware in communication with the data processing hardwareand storing instructions that when executed by the data processinghardware cause the data processing hardware to perform operationscomprising: receiving audio data corresponding to a first utterancespoken by a user associated with the computing device, the firstutterance comprising a default hotword followed by a command to playbackmusic from the computing device; detecting the default hotword in theaudio data corresponding to the first utterance spoken by the user, thedetection of the default hotword in the audio data causing a speechrecognizer to perform speech recognition on the audio data to identifythe command to playback the music from the computing device; in responseto the speech recognizer performing speech recognition on the audio datato identify the command to playback the music, executing the command toplayback the music from the computing device; and during playback of themusic from the computing device: activating a set of additional hotwordseach associated with a respective action for controlling the playback ofthe music from the computing device; restricting the activated set ofadditional hotwords to a subset of the activated set of additionalhotwords based on a playback state during the playback of the music fromthe computing device; receiving additional audio data corresponding to asecond utterance spoken by the user, the second utterance comprising oneof the additional hotwords in the subset of the activated set ofadditional hotwords; detecting the additional hotword in the additionalaudio data corresponding to the second utterance spoken by the user; andbased on detecting the additional hotword in the additional audio datacorresponding to the second utterance, performing the respective actionassociated with the detected additional hotword for controlling theplayback of the music from the computing device.
 12. The computingdevice of claim 11, wherein detecting the default hotword in the audiodata corresponding to the first utterance comprises detecting thedefault hotword in the audio data without performing speech recognitionon the audio data.
 13. The computing device of claim 11, wherein thespeech recognizer executes on the data processing hardware of thecomputing device.
 14. The computing device of claim 11, wherein theoperations further comprise, in response to detecting the defaulthotword in the audio data corresponding to the first utterance spoken bythe user, providing the audio data corresponding to the first utteranceto a server in communication with the data processing hardware, theserver executing the speech recognizer to perform the speech recognitionon the audio data to identify the command to playback the music from thecomputing device.
 15. The computing device of claim 11, whereindetecting the additional hotword in the additional audio datacorresponding to the second utterance comprises detecting the additionalhotword in the additional audio data without performing speechrecognition on the additional audio data.
 16. The computing device ofclaim 11, wherein detecting the additional hotword in the additionalaudio data corresponding to the second utterance comprises: extractingaudio features of the additional audio data that corresponds to thesecond utterance; generating, using a hotword detector, hotwordconfidence score by processing the extracted audio features;determining, by the hotword detector, whether the hotword confidencescore satisfies a hotword confidence threshold; and when the hotwordconfidence score satisfies the hotword confidence threshold,determining, by the hotword detector, that the additional audio datacorresponding to the second utterance includes the additional hotword.17. The computing device of claim 16, wherein the operations furthercomprise, when the hotword confidence score fails to satisfy the hotwordconfidence threshold: determining, by the hotword detector, that theadditional audio data does not include the additional audio datacorresponding to the second utterance does not include the additionalhotword; and bypassing performing the respective action for controllingthe playback of the music from the computing device.
 18. The computingdevice of claim 11, wherein the second utterance only comprises the oneof the additional hotwords in the subset of the activated set ofadditional hotwords.
 19. The computing device of claim 11, wherein eachadditional hotword in the activated set of additional hotwords isassociated with a respective hotword model configured to recognize audioof the respective additional hotword.
 20. The computing device of claim11, wherein the operations further comprise storing multiple hotwordmodels on the memory hardware of the computing device, each hotwordmodel of the multiple hotword models associated with a respective one ofthe additional hotwords in the activated set of additional hotwords thatis configured to recognize audio of the respective one of the additionalhotwords.